152 research outputs found
Fabrication and characterization of superconducting circuit QED devices for quantum computation
We present fabrication and characterization procedures of devices for circuit
quantum electrodynamics (cQED). We have made 3 GHz cavities with quality
factors in the range 10^4--10^6, which allow access to the strong coupling
regime of cQED. The cavities are transmission line resonators made by
photolithography. They are coupled to the input and output ports via gap
capacitors. An Al-based Cooper pair box is made by ebeam lithography and Dolan
bridge double-angle evaporation in superconducting resonators with high quality
factor. An important issue is to characterize the quality factor of the
resonators. We present an RF-characterization of superconducting resonators as
a function of temperature and magnetic field. We have realized different
versions of the system with different box-cavity couplings by using different
dielectrics and by changing the box geometry. Moreover, the cQED approach can
be used as a diagnostic tool of qubit internal losses.Comment: 4 pages, 6 figures, Applied Superconductivity Conference 200
Measurement of a Vacuum-Induced Geometric Phase
Berry's geometric phase naturally appears when a quantum system is driven by
an external field whose parameters are slowly and cyclically changed. A
variation in the coupling between the system and the external field can also
give rise to a geometric phase, even when the field is in the vacuum state or
any other Fock state. Here we demonstrate the appearance of a vacuum-induced
Berry phase in an artificial atom, a superconducting transmon, interacting with
a single mode of a microwave cavity. As we vary the phase of the interaction,
the artificial atom acquires a geometric phase determined by the path traced
out in the combined Hilbert space of the atom and the quantum field. Our
ability to control this phase opens new possibilities for the geometric
manipulation of atom-cavity systems also in the context of quantum information
processing.Comment: 5 + 6 page
Primary thermometry of propagating microwaves in the quantum regime
The ability to control and measure the temperature of propagating microwave
modes down to very low temperatures is indispensable for quantum information
processing, and may open opportunities for studies of heat transport at the
nanoscale, also in the quantum regime. Here we propose and experimentally
demonstrate primary thermometry of propagating microwaves using a transmon-type
superconducting circuit. Our device operates continuously, with a sensitivity
down to photons/\sqrt{\mbox{Hz}} and a bandwidth of 40 MHz.
We measure the thermal occupation of the modes of a highly attenuated coaxial
cable in a range of 0.001 to 0.4 thermal photons, corresponding to a
temperature range from 35 mK to 210 mK at a frequency around 5 GHz. To increase
the radiation temperature in a controlled fashion, we either inject calibrated,
wideband digital noise, or heat the device and its environment. This
thermometry scheme can find applications in benchmarking and characterization
of cryogenic microwave setups, temperature measurements in hybrid quantum
systems, and quantum thermodynamics
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